Motherboard Form Factors: AT, ATX

Motherboard Overview

• The motherboard is a fundamental component of a computer.

Form Factors

• The form factor determines a motherboard's layout and dimensions.
• Motherboards generally have a rectangular shape but vary in size and built-in components.
• A PC's case and power supply are related to the form factor and must have matching connectors to the motherboard.
• Standard form factors include AT, Baby AT, LPX, NLX, ATX, and BTX, along with variations.
• Most PC cases are designed for a single form factor.

AT Form Factor

• AT stands for Advanced Technology and is also known as Full AT.
• AT is now obsolete.
• IBM invented the AT form factor in the early 1980s, and it was the predominant form factor through the mid-1990s.
• The processor, memory, and expansion slots are aligned in the AT form factor.
• AT had a large keyboard port.
• A limited number of external ports presented a problem, as the only devices plugged into an average PC were a monitor and a keyboard.
• AT had to be replaced as more devices were connected to PCs.
• Motherboards catered to only a monitor and keyboard, unlike today's average PC, which includes a keyboard, mouse, printer, speakers, monitor, and USB devices.
• As technology improved the demand increased for smaller PCs.
• Manufacturers created smaller motherboards by placing the same components in a smaller area called Baby AT.
• Baby AT had problems with component placement, which resulted in limited expandability and overheating.

LPX and NLX Form Factors

• The demand for new standard form factors arose as new components were added.
• LPX (Low Profile Extended) was one successful slimline factor and was later replaced with NLX (New Low Profile eXtended).
• A small riser exists in the center of the form factor, where cards are horizontally attached to optimize space use.

ATX Form Factor

• ATX stands for Advanced Technology Extended.
• ATX addressed the demand for a new form factor with more standard connectors and flexibility.
• The ATX form factor was created in 1995.
• It started slowly but became the most commonly used form factor, surpassing AT by around 1998.
• The ATX form includes many improvements over AT.
• Better air movement is enabled by the placement of the power supply.
• CPU and RAM placement allows for easier access.
• RAM is placed closer to the Northbridge and CPU, improving performance over AT boards.
• PS/2 ports were introduced as new, smaller keyboard and motherboard ports.
• The ATX motherboards use soft power and can be turned on and off with soft power.
• ATX power switches comprise only a pair of small wires leading to the motherboard, unlike the thick power cords used in AT systems.
• Later version of ATX include microATX and FlexATX, with the latter being the smallest.

BTX Form Factor

• BTX stands for Balanced Technology Extended.
• BTX was introduced because heat remained a problem with faster CPUs and powerful graphics cards, even with improved ventilation.
• BTX aims to be the coolest form factor through design changes made to improve cooling by managing heat with a single airflow.
• Major design changes of BTX form factor include:
  • The I/O Ports and expansion slots have changed position.
  • The CPU has been moved to be at the front of the motherboard to get cool air from the front of the case.
  • Introduced a new fan & heatsink system called the thermal unit.
  • The thermal unit blows air directly outside of the case, unlike the fan in the ATX, which blows air inside of the case. -BTX is available in BTX, micro BTX, and picoBTX versions.

Chipsets

• Every motherboard has a chipset.
• The chipset defines many aspects of the motherboard, like processor and memory type support, and what internal and external devices the motherboard can support.
• Chipset features, performance, and stability vary greatly and are crucial in purchasing or recommending a motherboard.
• Chipsets facilitate communication between the CPU and other system devices
• Chipset components are relatively centralized on the motherboard.
• Most modern chipsets consist of Northbridge and Southbridge chips.

Northbridge & Southbridge

• The Northbridge chip handles AGP and memory communications.
• Northbridge chips deal heavily with memory and therefore require heatsinks.
• The Southbridge chip manages onboard peripherals like audio, storage drives, networks, and expansion buses.
• Most Southbridge chips do not need heatsinks.
• The Northbridge is responsible for high-speed components, while the Southbridge is responsible for low-speed components.

Chipset Manufacturers

• Both Intel and AMD create chipsets
• They lead the market despite competition from VIA Technologies and NVIDIA Corporation.
• Chipset manufacturers do not always use the terms Northbridge and Southbridge, and may use their own chip names.
• AMD uses the terms Northbridge and Southbridge, while Intel uses Memory Controller Hub and I/O Controller Hub respectively.